Donald Savage
Headquarters, Washington, DC January 13, 2000
(Phone: 202/358-1547)
Steve Roy
Marshall Space Flight Center, Huntsville, AL
(Phone: 256/544-6535)
Bill Steigerwald
Goddard Space Flight Center, Greenbelt, MD
(Phone: 301/286-5017)
Dr. Wallace Tucker
Harvard-Smithsonian Center for Astrophysics, Cambridge, MA
(Phone: 617/496-7998)
RELEASE: 00-10
CHANDRA RESOLVES X-RAY GLOW INTO MILLIONS OF OBJECTS
While taking a giant leap toward solving one of the greatest
mysteries of astronomy, NASA's Chandra X-ray Observatory also may
have revealed the most distant objects ever seen in the Universe
and discovered two puzzling new types of cosmic objects.
Not bad for being on the job only five months.
Chandra has resolved most of the X-ray background, a
pervasive glow of X-rays throughout the Universe, which was first
discovered in the early days of space exploration. Before now,
scientists have not been able to discern the origin of the hard,
or high-energy, X-ray background, because until Chandra no
telescope has had the technology to resolve it.
"This is a major discovery," said Dr. Alan Bunner, Director
of NASA's Structure and Evolution of the Universe science theme.
"Since it was first observed 37 years ago, understanding the
source of the X-ray background has been a Holy Grail of X-ray
astronomy. Now, it is within reach."
The results of the observation will be presented today at the
195th national meeting of the American Astronomical Society in
Atlanta, GA. An article describing this work has been submitted
to the journal Nature by Dr. Richard Mushotzky of NASA's Goddard
Space Flight Center, Greenbelt, MD, Drs. Lennox Cowie and Amy
Barger at the University of Hawaii, Honolulu, and Dr. Keith Arnaud
of the University of Maryland, College Park.
"We are all very excited by this finding," said Mushotzky.
"The resolution of most of the hard X-ray background during the
first few months of the Chandra mission is a tribute to the power
of this observatory and bodes extremely well for its scientific
future."
The Chandra team looked at a small section of the sky, a
circle about one-fifth the size of a full moon, and resolved about
80% of the X-ray glow in this region into specific light sources.
Stretched across the entire sky, this adds up to approximately 70
million sources, most of which are galaxies.
One-third of the sources are galaxies whose cores shine
bright in X-rays, yet do not shine in visible light. There may be
tens of millions of these "veiled galactic nuclei" in the
Universe. Each of these galaxies likely harbors a massive black
hole at its core that produces X-rays as gas is pulled toward it
at nearly the speed of light.
A second new class of objects, comprising approximately one-
third of the sources, is assumed to be "ultra-faint galaxies."
Mushotzky said that these sources may emit little or no optical
light, either because the dust around the galaxy blocks the light
totally or because the optical light is eventually absorbed during
its long journey across the Universe.
In the latter scenario, Mushotzky said that these sources
would be well over 14 billion light years away and thus the
earliest, most distant objects ever identified.
Resolution of the X-ray background relied on a 27.7-hour
Chandra observation using the Advanced CCD Imaging Spectrometer in
early December 1999, and also utilized data from the Japan-U.S.
Advanced Satellite for Cosmology and Astrophysics.
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